"Ratio" in English has two meanings, which in Italian can be rendered as "rapporto" in one case, and "proporzione", which I think is translated exactly by the English word "proportion".

The first case, rapporto, or quoziente, is expressed with / or something to that effect.

If I say that 4/5 of APUG forum participants do not write in proper unambiguous English the second member, the divisor, is the "total"* of the two groups of APUG participants, and the first, the dividend, is those for each five participants who cannot use unambiguous English.

If I say that the proportion between those who can use unambiguous English and those who cannot is 1:4, I say the same thing expressed as a proportion.

Those two kinds of notation, 1:4 and 1/5 or 4:1 and 4/5 are, if I get it right, both termed "ratio" in English.

This is made worse by the fact that / and : are alternative signs for "division", and although it is customary to use / for "rapporto" and : for "proportion" this subtleties can go lost for writers of instruction booklets.

A trained person always reads 1:10 as "one to ten" (eleven parts in total) but many would read it as 1/10. It would be called a "ratio" in both cases correctly but the dilution would be different.

I guess in Italian and in other languages the ambiguity would be resolved because it would be specified "a proportion of 3:10" or "un quoziente di 3/13". In English you are pretty much stack with "ratio" which is "irrational" a way to express oneself (quotient, proportion should find larger use).

The ":" is never used alone for division. It is formed from a dash through the colon (terrible double meaning here! ). The notation 1/10 is still one tenth which is 10% or 1 + 9 or 1:9. More a function of math than English I think.

Regardless of the measurement units used, Grams, Ounces, Millifarkles or whatever, the ratios always came out right using YOUR units. And, they made up molal solutions not molar. So, that is the origin of many of our formulas and procedures. Everything was assumed to be in ratios or parts, not the native measures.